Present day document handling and counting apparatus have the capability of accurately handling and counting sheets at high speed. Typically, sheets placed in an infeed hopper are separated from a stack fed on a one-at-a-time basis and at spaced intervals, the difference in transmissivity of the gap between separated sheets and the sheets themselves being utilized for counting purposes. Present day handling and counting apparatus typically operates under control of manually operable switches and buttons to perform the desired operations. For example, the apparatus is normally turned on by operating an on/off switch to the on position and operating a start switch or button to turn on the document handling apparatus. Sheets placed in the infeed hopper are separated, counted and collected at an output stacker. During normal counting, the count developed in a display counter will be retained until it is manually reset. Thus, for example, the sheets placed in the infeed hopper are separated, counted and delivered to the output stacker. If the contents of the output stacker are removed and again PG,3 placed into the infeed hopper, the count will be double that of the original count, unless the count has been manually reset. Also the handling apparatus will not be turned off unless a stop button is operated.
When counting sheets in present day apparatus, unless the sheets are accurately aligned, the feeding of sheets in a skewed manner will yield an erroneous count. In addition, even among those document handling and counting devices presently capable of detecting the presence of double-fed sheets, it is extremely difficult to differentiate between two clean double-fed sheets and one dirty sheet. This capability is of great value in the counting of paper currency.